1. Field of the Invention
The present invention generally concerns (i) processes for making composite laminate materials from multiple sheets of thin metals; (ii) laminate composite materials so made; and (iii) uses of the laminate composite materials so made, particularly in lightweight armor.
The present invention particularly concerns (i) processes for making in air in a heated load press composite laminate materials at large size and low cost, including in contoured form; (ii) composite laminate materials having large numbers of (a) tough metal layers interleaved with (b) hard intermetallic regions; and (iii) the tailoring of hard composite laminate materials for use, among other applications, as lightweight vehicular and body hard armor.
2. Description of the Prior Art
2.1 Armor
The following discussion, and facts, are presently, circa 1998, available at many sites on the Internet. The following materials of this section 2.1 are in particular derived from information available, circa 1998, at the web site of Armor Technology Corporation, www.armortechnology.com.
2.1.1 Armor
Armor is a protective xe2x80x98skinxe2x80x99, or plating for protection of an underlying structure. There are basically three types of armor. Homogenous armor has the same hardness throughout. Face-hardened armor has an extremely hard outer layer while the rest is hard, but less brittle. Laminated armor is made up of several hard layers of material, such as steel, titanium, ceramics, etc.
Tanks and other military vehicles use abundant armor. Armor is also used in armored land combat vehicles, structural shields, load bearing security walls, armored cars and other commercial vehicles, high speed trains, cash carrying vehicles (especially as all-around protection); private cars (most usually in door and floor panels); financial institutions particularly in security doors, partitions and briefcases; private homes particularly in front doors, walls and partitions; helicopters and light aircraft particularly in seats, doors, panels, channels; and boats and small ships particularly in superstructures, cabins and control rooms.
Composite armors are efficient structural materials that also provide outstanding protection against ballistic projectiles. They were originally developed for military armored vehicles to eliminate the need for parasitic armor.
2.1.1 Background of Body Armor
The rationale for body armor is well established. As well as its obvious application in warfare, every year about 60 sworn police officers are shot to death in the United States in the line of duty. At the same time, about 20 are saved by wearing armor. Had all the officers shot in recent years been wearing armor when shot, another 15 per year would likely have been saved from fatal gunshot wounds, roughly doubling the present number saved, and more than 15 others would likely have been saved from death by other causes.
Most police officers serving large jurisdictions report they have armor and wear it at all times when on duty and clearly identifiable as police officers. The kind of armor usually worn is soft armor, which is designed to be concealablexe2x80x94most styles are undergarmentsxe2x80x94and comfortable enough to be worn routinely. Such armor is designed for protection from handgun bullets but not from rifle bullets or edged or pointed weapons such as knives or icepicks. The distinctive, nonconcealable xe2x80x9ctacticalxe2x80x9d armor worn by police SWAT (Special Weapons and Tactics) teams for protection from rifle bullets as well as pistol bullets is more familiar to many laymen. This latter type of xe2x80x9chardxe2x80x9d personal armor is the type of armor supported by the advanced materials of the present invention, which are very lightweight but rigid.
Lightweight, composite, body armor preferably protects effectively against not only most known small-arms, as at present, but also against high velocity ballistic threats. Optional plate inserts presently provide some extra level of protection against rifle bullets, but are not presently of practical size and weight for extended wear.
A comfortable, ergonomic, body armor product would preferably accord the wearer maximum comfort even during prolonged periods of wear. At least front and back protection should be provided. The armor garment would desirably not contribute to heat stress of the wearer, but would readily accommodate physical effort by the wearer.
2.1.2 Summary of NIJ Standard 0101.03
The National Institute of Justice (NIJ) standard 0101.03 is of relevance to the present invention because, as will be explained, the materials of the invention are readily used in construction of, among diverse other forms of armor, xe2x80x9chardxe2x80x9d body armor. The body armor so constructed, although lightweight at about 3.0 to 4.5 grams per cubic centimeter, is potentially capable of meeting NIJ standard 0101.03 type IV, as explained below. It is the first practical body armor of both such (i) thinness and (ii) light weight known to the inventors to potentially so meet this standard. For example, it will be found in this specification disclosure that the 0.2 inch thickness of the new material has reliably stopped high-power penetrating rounds (of the types explained below) that will penetrate xc2xexe2x80x3 of hard steel armor, which steel armor is, of course, also much more dense.
The National Institute of Justice (NIJ) standard 0101.03 is a performance standard, not a construction standard. It does not specify the area of coverage, nor does it specify any material to be used in the armor. The standard is thus directed to permitting and encouraging technical innovation, including the development of materials and designs providing better ballistic resistance, greater comfort, or lower cost. However, some aspects of the standard were introduced specifically to provide stringent tests of likely weak points of Kevlar fabric armor, which at the time was almost the only type of concealable body armor marketed in the United States.
NIJ notes that xe2x80x9cFor the purposes of the . . . body armor certification procedures, the following definitions have been adopted:
A body armor MODEL is a manufacturer designation that identifies a unique ballistic panel construction; i.e., a specific number of layers of one or more types of ballistic fabric and or ballistic-resistant material assembled in a specific manner.
A body armor STYLE is a manufacturer designation (number, name, or other descriptive caption) used to distinguish between different configurations of a body armor product line each of which includes the same model of ballistic panel.
The 0.03 standard defines six standard types of ballistic resistance for which armor may be tested and provides for custom testing for xe2x80x9cspecial typexe2x80x9d ballistic resistance. Each type is defined in terms of the type or types of bullets fired at panels of the armor to test its ballistic resistance (see table 1, following). Two types of handgun bullets are fired to test for Type I, II-A, II, or III-A ballistic resistance, which soft armor can provide. One type of rifle bullet is fired to test for Type III or IV ballistic resistance, which hard armor can provide.
Each standard type of armor is expected to offer protection against the threat associated with it as well as against the threats associated with all other standard types of armor appearing above it in table 1. For this reason, the types of armor defined by NIJ Std.-0101.03 are often referred to as xe2x80x9clevels,xe2x80x9d level II-A being presumably superior to level I, for example. However, a certification test for type II-A ballistic resistance would not actually test resistance to type I threats. In addition, an NIJ guide specifies other threats against which it expects armor of each standard ballistic-resistance level to provide protection (see table 2), even though the 0.03 test does not actually test resistance to such threats.
SOURCE: National Institute of Justice, 1987.
SOURCE: National Institute of Justice, 1987 [144] and 1989 [145].
The NIJ standard specifies that xe2x80x9cFour complete armors, selected at random and sized to fit a 117 cm (46 in) to 122 cm (48 in) chest circumference, shall constitute a test sample. (Note: The larger the size, the more likelihood that all ballistic testing will fit on just two complete armors.) In quality assurance, xe2x80x9cselected at randomxe2x80x9d usually means xe2x80x9cselected at random with uniform probabilityxe2x80x9dxe2x80x94i.e., sampling should ensure that all units of the model should have the same chance of being selected to be tested. However, this is impossible if samples are selected for certification testing before production of the model has been discontinued. Typically samples are selected after only a few units have been produced; consequently, the sampling procedure does not guarantee that the samples are representative of yet-to-be-produced units of the model, particularly of smaller sizes.
Armor to be tested is mounted on a flat block of inelastic backing materialxe2x80x94typically modeling clayxe2x80x94to be shot. The impact velocity of each bullet is measured using a ballistic chronograph. If the bullet hits an appropriate point on the panel at an impact velocity within specified limits (see table 1), then the impact is considered a fair hit. The test requires a fair hit in each of six specified areas on each panel in a specified sequence (see the diagrammatic representation in the next following paragraph). Each shot must impact at least 3 inches from the edge of the panel and at least 2 inches from the closest point of impact of any prior shot.
The sequence of aim points on each panel, as specified in NIJ Standard 0101.03, looks like the following diagrammatic representation.
All shots must be at least 7.6 cm (3 in) from any edge and at least 5 cm (2 in) from another shot. The source for this information is the National Institute of Justice, 1987.
In tests of Type I, II-A, II, or III-A ballistic resistance, four complete armors, typically including eight armor panels (four each front and back) are usually shot. Each ballistic element (front or back panel) is sprayed with water and then shot with test bullets of the first type, then another one is sprayed and shot with test bullets of the second type. This is repeated with un-sprayed, dry samples. This requires a minimum of 48 shots per test: 2 element types (front and back)xc3x976 shots eachxc3x972 types of bulletsxc3x972 wetness conditions.
If the velocity of a shot is too low and it does not penetrate the panel, or if the velocity of a shot is too high and it does penetrate the panel, then the shot is repeated, aimed at least 2 inches from the closest point of impact of any prior shot. However, in more than eight shots (of one caliber) may be fired at any panel. The armor cannot be certified if any fair shot penetrates.
After the first fair shot at each panel, the panel is removed from the backing and the depth of the crater (called the backface signature or BFS) is measured. If the BFS exceeds 44 mm or if the armor was penetrated, it fails; if not, the panel is replaced on the backing without filling the crater or otherwise reconditioning the backing material, and testing for penetration is resumed. (10) The standard prohibits adjusting the panel (e.g., patting it down) thereafter, unless it is reused for testing with a second type of bullet.
2.2 Specific Previous Materials
Certain previous materials relevant to the present invention are discussed in the following sections. The section headings are for convenience only, and the materials described within the section may be relevant to the present invention in any of the manner of fabrication, the existence of intermetallic regions, the particular metals used and/or compounded, and/or other factors not clearly delimited in the section headings. A greater appreciation of the diverse, but generally remote, relevance of the following references to the present invention may potentially be gained if the present invention is first understood, and the following references and previous materials only then considered (reconsidered).
2.2.1. Aluminum, Titanium, and Steel; and Aluminum, Titanium, Titanium-Aluminum or Steel Intermetallics
The present invention will be found to concern a hard intermetallic compound preferably having as one of its constituent components aluminum. If is known in metallurgy that intermetallic compounds of aluminum, a relatively soft metal, can be hard.
There are many ways to derive intermetallic compounds. For example, U.S. Pat. No. 5,098,469 to Rezhets issued Mar. 24, 1992 for a POWDER METAL PROCESS FOR PRODUCING MULTIPHASE NIxe2x80x94ALxe2x80x94TI INTERMETALLIC ALLOYS and assigned to General Motors Corporation (Detroit, Mich.) concerns a powder metallurgy process for producing near-net shape, near-theoretical density structures of multiphase nickel, aluminum and/or titanium intermetallic alloys. The process employs pressureless sintering techniques, and consists of blending a brittle aluminide master alloy powder with ductile nickel powder, so as to achieve the desired composition. Then, after cold compaction of the powdered mixture, the compact is liquid phase sintered. The four-step liquid phase sintering process is intended to ensure maximum degassing, eliminate surface nickel oxide, homogenize the alloy, and complete densification of the alloy by liquid phase sintering.
The intermetallic compound, and regions, of the composite laminate material of the present invention will be seen to be produced from foils, or thin sheets, of different metals. U.S. Pat. No. 5,256,202 to Hanamura, et. al. issued Oct. 26, 1993 for a Tixe2x80x94Al INTERMETALLIC COMPOUND SHEET AND METHOD OF PRODUCING SAME assigned TO NIPPON STEEL CORPORATION (Tokyo, JP) concerns a Tixe2x80x94Al intermetallic compound sheet of a thickness in the range of 0.25 to 2.5 mm formed of a Tixe2x80x94Al intermetallic compound of 40 to 53 atomic percent of Ti, 0.1 to 3 atomic percent of at least one of material selected from the group consisting of Cr, Mn, V and Fe, and the balance of Al, and a Tixe2x80x94Al intermetallic compound sheet producing method comprising the steps of pouring a molten Tixe2x80x94Al intermetallic compound of the foregoing composition into the mold of a twin drum continuous casting machine, casting and rapidly solidifying the molten Tixe2x80x94Al intermetallic compound to produce a thin cast plate of a thickness in the range of 0.25 to 2.5 mm and, when necessary, subjecting the thin cast plate to annealing and HIP treating. The Tixe2x80x94Al intermetallic compound sheet is stated to have excellent mechanical and surface properties.
2.2.2. Layered Armor
The composite material of the present invention, suitable for use as armor, will be seen to have regions, or layers (albeit without sharp boundaries) of differing materials. It has been known since ancient times to make armor in layers where each layer imparts some particular quality to the armor. Most recently the incorporation of hard ceramics in armor has been much pursued.
An exemplary U.S. Pat. No. 4,836,084 to Vogelesang, et. al. Jun. 6, 1989 for ARMOR PLATE COMPOSITE WITH CERAMIC IMPACT LAYER. This patent concerns an armor plate composite composed of four main components, viz. the ceramic impact layer, the sub-layer laminate, the supporting element and the backing layer. The ceramic impact layer is asserted to be excellently suitable for blunting the tip of a projectile. The sub-layer laminate of metal sheets alternating with fabrics impregnated with a viscoelastic synthetic material is perfectly suitable to absorb the kinetic energy of the projectile by plastic deformation, sufficient allowance for said plastic deformation being provided by the supporting honeycomb shaped layer. The backing layer away from the impact side and consisting of a pack of impregnated fabrics still offers additional protection. The optimum combination of said four main components is said to give a high degree of protection of the resulting armor plate at a limited weight per unit of surface area.
There is also present interest in putting high-strength fibers into composite materials suitable for armor. U.S. Pat. No. 5,635,288 to Park issued Jun. 3, 1997, for a BALLISTIC RESISTANT COMPOSITE FOR HARD-ARMOR APPLICATION concerns a ballistic resistant composite for hard-armor application. The composite includes a rigid plate, and a ballistic laminate structure supported by the plate. The laminate structure includes first and second arrays of high performance, unidirectionally-oriented fiber bundles. The second array of high performance, unidirectionally-oriented fiber bundles is cross-plied at an angle with respect to the first array of fiber bundles, and is laminated to the first array of fiber bundles in the absence of adhesives or bonding agents. First and second polymeric films are bonded to outer surfaces of the laminated first and second arrays of unidirectional fiber bundles without penetration of the films into the fiber bundles or through the laminate from one side to the other. Thus, a sufficient amount of film resides between the laminated first and second arrays of unidirectional fiber bundles to adhere the first and second arrays of fiber bundles together to form the ballistic laminate structure.
A combination of both the concepts of (i) intermetallic phase regions, and (ii) layers is shown in U.S. Pat. No. 4,853,294 to Everett, et. al. issued Aug. 1, 1989 for CARBON FIBER REINFORCED METAL MATRIX COMPOSITES and assigned to United States of America as represented by the Secretary of the Navy (Washington, D.C.). This patent concerns an improved metal, alloy, or intermetallic matrix composite containing carbon reinforcing fibers. The carbon reinforcing fibers are protected from interaction with the matrix material by an inner and an outer barrier layer. The outer layer is any one of the group of stable, non-reactive ceramic materials used to protect fibers, and the inner layer is a ductile, low density, oxygen desorbing rare earth metal. The carbon fibers are particularly useful in forming composites with a titanium aluminide matrix.
2.3 Why Hard Armor Fails
The failure of hard armor, and its penetration by projectiles, is enhanced when the speed of sound in the hard material of the armor is greater than the speed of the penetrating projectile, as is most often the case. Cracks propagate in the armor at the speed of sound (in the material of the armor), fragmentation occurs, and fragments are displaced from in front of the projectile before complete, energy-absorbing, deformation of these fragments by the projectile has occurred.
For example, the hardness of ceramic is unexcelled (save by diamond, and other rare materials not presently practical for armor). It is generally accepted that the ability of ceramic armor to defeat penetration by a projectile can be enhanced if the armor is confinedxe2x80x94i.e., kept in place during impactxe2x80x94in order to limit fragmentation and fragment dispersion. However, in real ballistic events providing such confinement to ceramics is difficult and expensive to achieve.
The present invention will be immediately next seen to concern a materialxe2x80x94a composite laminate material produced by a new, but simple, processxe2x80x94where a hard, ceramic-like, component is xe2x80x9ckept in placexe2x80x9d even during attempted penetration of the material by a high-speed projectile. Moreover, the flight of a projectile attempting penetration is significantly xe2x80x9cinterfered withxe2x80x9d, both in direction and in the orientation of the projectile, by the new material to the detriment of penetration of the material by the projectile.
The present invention contemplates a process of making (i) under modest pressure and (ii) at modest temperature (iii) in air a composite laminate material from sheets, or foils, of (i) a tough first metal initially interleaved with sheets, or foils, of (ii) a second metal that is suitably compounded with the first metal during the process to produce, ultimately, a very hard intermetallic region, or layer.
The present invention further contemplates that the composite laminate material so made can serve as hard armor where the very hard intermetallic, ceramic-like, regions or layers of the material are confined, and are held in place even under great stress, by dint of being xe2x80x9csandwichedxe2x80x9d between tough metal layers. The confinement makes that any such fragmentation of the hard intermetallic layer by a high-energy impinging projectile as will inevitably occur will but poorly serve to displace the resulting hard fragments from in front of the projectile, forcing the projectile to interact with these hard fragments and limiting its penetration.
Moreover, and importantly, the tough metal layers serve to limit the cracking and fracturing of the hard intermetallic regions, or layers, in the first place (i) by blunting the propagation of cracks and fractures at the boundaries between the metal layers and intermetallic regions, and (ii) by channeling such cracks and fractures of the intermetallic regions as do occur in directions orthogonal to the axis of projectile impact (where they do little to promote projectile penetration)xe2x80x94instead of along the axis of impact (where penetration might be assisted). In simple terms, fracture cracks are hard to form in the composite laminate material of the present invention, and those that do form so form in the wrong directions to effectively remove (hard) fractured material from in front of an impinging projectile.
Moreover, the fracture cracks that form in the plane of the composite laminate material (or armor), and sideways to the path of the impinging projectile (instead of ahead of the projectile), do not evenly so form in either (i) space or (ii) time. The fracture cracks are not evenly angularly distributed about the point of projectile impact. Neither do they progress in a radially straight path, or any straight path, from the point of impact in any fracturing region. The fracture cracks do not even proceed along substantially identical paths as such cracks arise (with progressive penetration of the projectile) in successively deeper regions of the composite laminate material (or armor). This means that those crooked, non-straight, fracture cracks that do form do not identically so form over time. It is even believed that the sideways fracture cracks that are irregular in each of location, path, direction, and consistency do not even form at the same rate, nor at exactly the same times within laminate layers.
The exceedingly irregular spatial and, it is believed, temporal irregularity in formation of the fracture cracks interacts with the impinging projectile. The (significant, large) energy for the formation of the sideways irregular fracture cracks comes, of course, from the kinetic energy of the projectile. When this projectile energy is tapped first in one sideways direction to one extent at one time, and then in another, nearly random, sideways direction to another extent at another, pseudo-random, time, then these irregularly-occurring transverse perturbations to the projectile tend to severely disrupt its flight, and its penetration. The perturbations tend to turn the projectile (i) along its flight axis, and (ii) in its path of penetration (which are separate and different things). In somewhat exaggerated terms such as are, unfortunately, not precisely accurately descriptive of reality, it becomes as if a projectile attempting to penetrate hard material is forced to a sideways tilt with a wobble in the both the tilt angle and tilt direction while it attempts to penetrate along a meandering and crooked path (which path may not even be complimentary to the direction in which the projectile is tilted!) that changes over time (and at increasing depth of penetration).
All these spatial and temporal effects are devastating to the ability of the projectile to focus its energy on penetration. Spent projectiles have been recovered from the composite laminate material of the invention that have actually been turned sideways, and are penetrating substantially transversely to the original axis of impact. Although this xe2x80x9cturningxe2x80x9d is not alleged to be realizable for all combinations of composite laminate material versus projectile speed and energy (kinetic energy equals mass time velocity squared, E=mv2) , it is clearly quite a xe2x80x9ctrickxe2x80x9d to get any impinging high energy projectile turned sideways. Even if the projectile is not completely turned a full 90xc2x0 in its path of penetration, it is clearly very difficult, and requires great energy, to force a wobbling projectile sideways along a meandering indirect path through hard material. The composite laminate materials in accordance with the present invention are accordingly very useful as hard armor.
The propensity of the composite laminate material to xe2x80x9cturnxe2x80x9d the penetrating projectile can be still further improved if the laminate material is corrugated, in which mode the laminate material may be readily economically fabricated. For the rare case that the projectile hits centrally in the trough of a corrugation, it is possible to back one layer of corrugated armor with another that is offset, thus making it effectively impossible that a penetrating projectile should not be subject to significant flight-direction-distorting forces.
1. Method of Producing Laminate Composite Materials, Especially as are Useful for Hard Armor, in Accordance with the Present Invention
The present invention is based on a recognition that (i) no vacuum is needed, nor desired, in the reaction-sintering of metal foils so as to produce a quality intermetallic composite, and that the reacting of the foils should instead transpire in a hot-press furnace at atmospheric pressure and in the presence of atmospheric gases; oxidation not only presenting no problem but the oxygen and nitrogen gases from the atmosphere actually helping to produce a harder intermetallic compound.
The present invention is based on the further recognition that (ii) metal foils should not be quickly and explosively joined by the method of, or by exothermic reaction methods like, self-propagating high-temperature synthesis (xe2x80x9cSHSxe2x80x9d) as is commonly used for processing elemental metal powders into intermetallics, but that metal foils should rather first be pressured together, and then somewhat leisurely (by standards of the prior art) reacted over a period of, typically, some 10+ hours during which period temperature rises and the metals of the foils form an intermetallic compound and region. One foilxe2x80x94made of a metal that is subject to liquefaction at elevated temperature and that would otherwise flow from the reaction sitexe2x80x94becomes locked in place by solid state diffusion under pressure at a time before its melting temperature is reached. As the temperature is increased, this foil is totally reacted and consumed in making the intermetallic region, or layer.
Finally, the present invention is based on the still further recognition that the union of preferably large numbers of interleaved foils of two types of metal to produce a composite material should proceed until metal foils of one type are completely consumed, and are taken up into making an intermetallic compound with the metal foils of the other type, the composite laminate material ultimately produced thus consisting of (i) layers of the metal of a first type interleaved with (ii) intermetallic regions consisting of both the firstxe2x80x94and the second-type metals.
Therefore in one of its aspects the present invention is embodied in a method of making a composite laminate material. In the method (i) a number of first foils made from one or more first metals and metal alloys are interleaved with (ii) a number of second foils made from one or more second metals and metal alloys suitable to compound with the one or more first metal and metal alloys to produce a hard intermetallic compound.
The interleaved foils are reacted under heat and pressure in the presence of atmospheric gases so as to substantially completely react the one or more second metals and metal alloys with the one or more first metal and metal alloys, forming where each second metal foil had been a region of hard intermetallic compound.
Thus a composite laminate material having (i) layers of one or more first metals and metal alloys, interspersed with (ii) regions of an hard intermetallic compound, is made. (There are no layers of the second metal and metal alloys remaining; all the second metal and metal alloys are reacted.)
The first foils are preferably made from one or more first metals or metal alloys from the group consisting of titanium, nickel, vanadium, iron and alloys and combinations of titanium, nickel, vanadium and iron. The second foils are preferably made from one or more second metals and metal alloys from the group consisting of aluminum and alloys of aluminum.
In greater detail, the reacting under heat and pressure normally consists of first placing the interleaved first and second foils under pressure; then raising the temperature of the pressured interleaved foils to (i) less than a melting point of the one or more second metals and metal alloys but (ii) sufficiently high so that, at pressure, solid state diffusion occurs between the interleaved foils, physically locking the foils in place; then further raising the temperature of the pressured, diffused, locked interleaved foils until all the one or more second metals are reacted with the one or more first metals to form an intermetallic compound, this raising being done sufficiently slowly and under sufficient continuing pressure so that, despite the fact that the reacting proceeds with increasing difficulty and an ultimate high temperature reached is greater than a melting point of the one or more second metals, the one or more second metals remain initially locked in place and ultimately become reacted without squirting in liquid state from between the first foils; and then, finally, cooling to room temperature the composite laminate material as is made from (i) layers of one or more first metals and metal alloys, interspersed with (ii) regions of an hard intermetallic compound. Notably, each and all of the placing, raising, further raising, and cooling transpire in the presence of atmospheric gases. The second foils become completely reacted with the first foils nonetheless that the temperature of liquefaction of the at least one second metals and metal alloys from which the second foils are made is exceeded during the process.
Commonly the number of first and second foils is more numerous than 10, and are most commonly 20-100. The first and second foils commonly have thicknesses in the range of 0.1 mm to 1 mm, and most often less than 0.2 mm. All foils of a type, or all foils together, can have, but certainly need not have, the same thickness.
The maximum temperature of the reacting is commonly in the range from 600-800xc2x0 C. The pressuring is typically realized in a mechanical press, and more typically in a load press. The maximum applied pressure is typically in the range from 1-10 megapascals (1-10 MPa).
Although the in situ properties of the foils are difficult to measure, and must be estimated, the first foils (made from one or more first metals and metal alloys) typically have a plane strain fracture toughness, in the state of these first metals and metal alloys that is assumed to be, upon completion of the method, of greater than 40 MPa m. Meanwhile, the second metal foils (made from one or more second metals and metal alloys suitable to compound with the first metal and metal alloys) serve to produce an intermetallic compound having, typically, a Vickers microhardness of greater than 400 kg/mm2.
2. Penetration-resistant Composite Laminate Material
In another of its aspects, the present invention is embodied in a penetrationxe2x80x94resistant composite laminate materialxe2x80x94although strict attention must be paid to exactly what is meant by the words xe2x80x9ccompositexe2x80x9d and xe2x80x9claminatexe2x80x9d.
The composite material consists of a number of first metal layers, each consisting of one or more first metals and metal alloys, that have a high toughness, at least in the phase of the metals and metal alloys that is assumed within the final composite material. Notably, these first metal layers have and preserve this very high toughness because they are very thin. Should the layers be fused together as a monolithic thick plate then they would exhibit no where near this toughness.
The composite material further consists of a number of regions of intermetallic material interleaved with the first metal layers. This intermetallic material is not precisely in layersxe2x80x94although it is sometimes spoken of as being in layers; it actually constitutes the boundary regions between the metal layers themselves. This intermetallic regions consist of the first metals and metal alloys compounded with yet another, second, metal. The resultant compound, or intermetallic phase, typically has a Vickers hardness, at least as this material exists within the final composite, of greater than 400 kg/m2.
In summary, the metal layers, separated as they are by the intermetallic regions, have great toughness per unit weight. Meanwhile, the intermetallic regions, separated as they are by the metal layers, are very hard. The resulting composite laminate material is very tough and very hard, and is thus penetration resistant and suitable for use, among other applications, as armor.
Therefore in another of its aspects the present invention is embodied in a composite laminate material. The preferred composite laminate material consists of (i) a number of metal layers of one or more tough first metals or metal alloys interleaved with (ii) a number of regions, coextensive with the metal layers, of hard intermetallic material, each region consisting of the one or more first metals and metal alloys compounded with one or more second metals or metal alloys. The tough metal layers are thus separated by the hard intermetallic regions. Notably, no second metals or metal alloys exist in native form, all being within the material of the hard intermetallic region.
The one or more tough first metals and metal alloys are preferably drawn from the group consisting of titanium, nickel, vanadium and iron, and combinations of titanium, nickel, vanadium, and iron. The one or more second metals or metal alloys are preferably drawn from the group consisting of aluminum and alloys of aluminum.
The resulting composite laminate material typically has a density between 3 and 4.5 grams per cubic centimeter, and most commonly less that 4 grams per cubic centimeter.
The metal foils from which the layers are created need not be xe2x80x9claid upxe2x80x9d, and reacted, in the absence of mechanical stresses other than the pressuring, but may instead be squeezed, buckled and/or corrugated as desired. Resultantly, the composite laminate material will have such residual internal stresses between the metal layers and the intermetallic regions as may be useful in intentionally directionally deflecting a penetrating projectile.
Particularly when so used for body armor, but also in general, the composite laminate material may have and assume, as an incident of its fabrication, three-dimensional, non-planar, contour.
3. Armor
Therefore in yet another of its aspects the present invention will be recognized to be embodied in armor.
Armor in accordance with the present invention consists of a laminate composite material having (i) at least 10 metal layers, at least 100 cm2 in area, of at least one tough first metal or metal alloy; separated by and interleaved with (ii) at least 9 hard intermetallic regions, coextensive with the metal layers and thus at least 100 cm2 in area, of the at least one tough first metal or metal alloy compounded with at least one second metal or metal alloy. Thus tough metal layers are separated by the hard intermetallic regions. Notably, no appreciable second metals or metal alloys exist in native form, all being within the hard intermetallic material.
The at least one tough first metal or metal alloy is preferably drawn from the group consisting of titanium, nickel, vanadium and iron, and combinations of titanium, nickel, vanadium, and iron. The at least one second metal or metal alloy is preferably drawn from the group consisting of aluminum and alloys of aluminum.
The armor typically has a density between 3 and 4.5 grams per cubic centimeter, and more typically less that 4 grams per cubic centimeter.
It may have residual internal stresses between the metal layers and the intermetallic regions, be conformed and adapted to non-planar contours. It is a strong candidate to meet the threat Level IV standard for body armor as defined by National Institute of Justice standard 0101.03 as of Jan. 1, 1998.
Although hard to measure, the metal layers normally have a 10 toughness greater than 40 MPa m while the regions of intermetallic material have a Vickers microhardness of greater than 400 kg/mm2.
Any of the metal layers and/or intermetallic regions may be of differing thickness. Such residual internal stresses as exist between the metal layers and intermetallic regions may serve to more substantially deflect a penetrating projectile from off its axis of impact than would be the case for the same penetrating projectile without the residual internal stresses.
The non-planar contours to which the composite laminate material is conformed and adapted may be: corrugations. Forming the material in the contour is a simple matter of laying up thin metal layers, or foils, that are corrugated before subjection the stack of metal layers, or foils, to heat and pressure. It is of no matter that slight air pockets and/or a slight mechanical mis-match of corrugated foils might initially exist in the stack. Everything forms into the solid composite material during processing.
The corrugated composite laminate material enjoys all the normal mechanical and strength advantages of corrugation. In other words, it may be capable of better supporting a load aligned with axis of corrugations in the plane of the material without buckling or bending. To this extent the utility of the material for construction, including for load-bearing walls and the sides of armored vehicles, is enhanced. Equally importantly, the corrugations help to turn the path of an impacting projectile. To account for the statistically small probability that the projectile should hit centrally in the trough of a corrugation, it is possible to back one panel of corrugated armor with another, offset, panel. If structural strength is desired in two perpendicular directions in the plane of a composite laminate material of the present invention, then corrugated panels of the material having their corrugations running in one direction may be alternated with other panels of the material having their corrugations running at a 90xc2x0 angle.
Practitioners of the building and structural materials arts will recognize that complex forms of the composite laminate material of the present invention may readily be designed, and built, for structural strength as well as inherent impact resistance. For example, the circular surround around the hinged access hatch lid on the turret of a tank is a complex form. It is clearly possible to xe2x80x9clay upxe2x80x9d sheets, or foils, to form composite laminate bodies having any of (i) a pre-cut central aperture and/or apertures for bolts, (ii) contours such as those of the hatch mating surfaces and of the turret, and (iii) regions that are relatively thicker, whether from foils that are regionally thicker or from regional use of more layers of foils. It is axiomatic that (i) complex forms can be efficiently built with the laminate process of the present invention, and (ii) the making of such complex forms in no way negates the essential strength advantages of material of the invention, particularly for use as armor.
4. Inexpensive High Performance Composite Materials
Accordingly, the present invention may still further be considered to be embodied in an economical material of exemplary properties.
In accordance with the present invention, first-metal films, normally 10 or more of 0.1 to 1.0 mm thickness of titanium, nickel, vanadium, and/or steel (iron) and alloys are interleaved with 9 or more second metal films, normally also 0.1 to 1.0 mm thickness, of aluminum or alloys thereof. Both films are economically commercially available.
The stacked metal films are conventionally heated to a modest 600-800xc2x0 C. while being pressured at a modest 1-10 megapascals, normally in the open air in a load frame. The composite material thus formed has (i) very tough first-metal layers separated by (ii) very hard intermetallic regions consisting of a compound of the first and second metals. The material density of, typically, 3 to 4.5 grams/cubic centimeter is both lightweight and strong to serve as armor.
As explained in the preceding section on armor, the composite laminate material may readily be formed in complex, three-demensional, shapes, generally including shapes with voids and cavities.
These and other aspects and attributes of the present invention will become increasingly clear upon reference to the following drawings and accompanying specification.